The heater in our '00 Concorde has a very strange problem. Since last winter the heater hasnt blown as hot as it used to. Tonight I noticed that when you come to a stop the air out of the vents gets considerably cooler, take off and the air heats back up. I also noticed this evening the temp gauge is reading a little warmer than usual, not much but enough to notice, usually runs about 3/8 on the temp gauge, tonight it was right at the halfway mark.

Any ideas?

Thank